Heat exchanger and method of assembly for automotive vehicles

ABSTRACT

A heat exchanger assembly includes at least one tube having an internal surface and an external surface, a composition cladding having at least lithium and magnesium applied to either one of the internal surface and external surface of the tube, and at least one component disposed adjacent the composition cladding, whereby the tube and component are joined together during a controlled atmosphere brazing process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to heat exchangers and, morespecifically, to a heat exchanger and method of assembly for anautomotive vehicle.

2. Description of the Related Art

It is known to provide automotive vehicles with heat exchangers such ascondensers, evaporators, heater cores and coolers. These heat exchangersare alternating rows of tubes or plates with convoluted fins made of ametal material such as aluminum or an aluminum alloy. Many of these heatexchangers have turbulators disposed within the tubes that requireinternal brazing. Previously, the tubes and turbulators have been brazedin a vacuum furnace. Recently, a process known as "controlled atmosphere(CAB)" furnace brazing has been used with non-corrosive fluxes. CABfurnace brazing has been preferred over vacuum furnace brazing due toimproved production yields, lower furnace maintenance requirements andgreater braze process robustness.

It is also known that the CAB furnace brazing currently used tomanufacture aluminum heat exchangers requires the use of fluxing agents,either chloride based or fluoride based. The use of these fluxing agentswith conventional aluminum heat exchangers promotes the dissociation anddisruption of the native aluminum oxide and magnesium oxide layerspresent on the surface of the aluminum heat exchanger to promote wettingof the molten clad layer between mating components.

It is further known for CAB furnace brazing that an inert gas such asnitrogen gas is used to provide a non-oxidizing atmosphere. Althoughconsidered to be non-oxidizing, nitrogen gas contains residualimpurities, most notably oxygen and water vapor. Although the aluminumheat exchanger is pre-cleaned using alkaline cleaning agents whichreduce the native aluminum oxide layer, the surface of the aluminum heatexchanger will re-oxidize in the CAB furnace due to the presence of theoxygen and water vapor in the nitrogen gas. To minimize reoxidation ofthe aluminum heat exchanger during the brazing process, the oxygen andwater vapor in the nitrogen gas may be purified to less than twentyparts per million (20 ppm).

Although CAB furnace brazing has worked well, it suffers from thedisadvantage that the internal tube surfaces and the turbulator of theheat exchanger require individual fluxing before assembly and an overallfluxing of the completed assembly before brazing. Also, CAB furnacebrazing suffers from the disadvantage that the individual fluxing of thecomponents of the heat exchanger is costly and time consuming. Further,CAB furnace brazing suffers from the disadvantage that purified inertgas is not cost effective for use in high volume processing of aluminumheat exchangers.

SUMMARY OF THE INVENTION

Accordingly, the present invention is a heat exchanger assembly for anautomotive vehicle including at least one tube having an internalsurface and an external surface, a composition cladding having at leastlithium and magnesium applied to either the internal surface or externalsurface of the tube, and at least one component disposed adjacent thecomposition cladding, whereby the at least one tube and the at least onecomponent are joined together during a controlled atmosphere brazingprocess.

Additionally, the present invention is a method of assembly of a heatexchanger for an automotive vehicle including the steps of providing atleast one tube having an internal surface and an external surface. Themethod includes the steps of applying a composition cladding having atleast lithium and magnesium to either one or both the internal surfaceor external surface. The method further includes the steps of disposingat least one component adjacent the composition cladding and joining thetube and component together using a controlled atmosphere brazingprocess.

One advantage of the present invention is that a heat exchanger assemblyis provided for an automotive vehicle that has a composition claddinghaving at least elemental lithium and magnesium that allows for fluxlessinternal brazing of the heat exchanger components without theapplication of a fluxing agent to promote oxide layer breakdown. Anotheradvantage of the present invention is that the heat exchanger assemblyeliminates the use of flux and is less expensive and less time consumingto manufacture. Yet another advantage of the present invention is that amethod of assembly of the heat exchanger is provided which eliminatesflux residues that can block internal tube passages. Still anotheradvantage of the present invention is that the heat exchanger assemblymay have the addition of elemental Cesium (Cs) in the compositioncladding to effectively promote aluminum and magnesium oxidedissociation and increased braze joint quality in a CAB furnace brazingprocess. A further advantage of the present invention is that theaddition of elemental Cesium in the composition cladding allows forhigher levels of Magnesium (Mg) in the core materials, thus providingstronger and more durable components. Yet a further advantage of thepresent invention is that the method uses an active metal getter sourceto remove residual gas impurities, namely oxygen and water vapor frominert gases to levels below 20 ppm for fluxless CAB furnace brazing ofthe aluminum heat exchanger assembly. Still a further advantage of thepresent invention is that the use of the active metal getter sourceallows fluxless CAB furnace brazing of evaporators, condensers, heatercores and radiators.

Other features and advantages of the present invention will be readilyappreciated as the same becomes better understood after reading thesubsequent description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of a heat exchanger assemblyaccording to the present invention.

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1.

FIG. 3 is an enlarged view of circle 3 in FIG. 2.

FIG. 4 is a schematic view of a method, according to the presentinvention, of assembly of the heat exchanger assembly of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, one embodiment of a heat exchanger assembly 10,according to the present invention, is shown. In this example, the heatexchanger assembly 10 is a condenser for an air conditioning system (notshown) of a vehicle such as an automotive vehicle (not shown) . Itshould be appreciated that the heat exchanger assembly 10 may be aparallel flow condenser, serpentine evaporator, heater core, ortransmission oil cooler.

Referring to FIG. 2, the heat exchanger assembly 10 includes at leastone, preferably a plurality of tubes 12. Each tube 12 extendslongitudinally and is generally rectangular in shape. Each tube 12 ismade of a core material having an internal surface 14 and an externalsurface 16. The internal surface 14 and external surface 16 each have acomposition cladding 18 thereon. The composition cladding 18 containslithium (Li) within a range from about 0.01% to about 0.3%, magnesium(Mg) within a range from about 0.2% to about 0.7%, sodium (Na) within arange from about 0.01% to about 0.1%, silicon (Si) within a range fromabout 4% to 13%, manganese (Mn) within a range from about 0% to about1%, copper (Cu) within a range from about 0.01% to 0.1%, zinc (Zn)within a range from about 0% to about 0.3%, beryllium (Be) within arange from about 0.01% to about 0.7%, impurities not exceeding a totalof 1%, balance aluminum. The core material of the tube 12 is made of analuminum based material selected from the Aluminum Association 1XXX,3XXX, 5XXX and 6XXX series aluminum alloys. It should be appreciatedthat the composition cladding 18 is made by rolling aluminum sheets ofdifferent alloys which is clad to the surfaces 14 and 16 of the tube 12by methods well known in the art.

Additionally, the composition cladding 18 may contain cesium (Cs) withina range from about 0% to about 2%. If Cesium is added to the compositioncladding 18, the lithium can be within a range from about 0.01% to about0.5%. The composition cladding 18 can be used with an aluminum brazematerial containing magnesium within a range from about 0.1% to about2.0%. It should be appreciated that the addition of elemental Cesium andLithium promotes aluminum and magnesium oxide dissociation in aluminumbraze materials.

Referring to FIGS. 1 through 3, the heat exchanger assembly 10 includesat least one component disposed adjacent the composition cladding 18.For example, the heat exchanger assembly 10 includes a turbulator 20disposed within the tube 12 adjacent the composition cladding 18 on theinternal surface 14. The turbulator 20 extends longitudinally andlaterally in a series of undulations. The turbulator 20 breaks up theflow through the tube 12 to effect heat transfer. In another example,the heat exchanger assembly 10 includes a fin 22 disposed adjacent thecomposition cladding 18 on the external surface 16. The fin 22 extendslongitudinally and laterally in a series of undulations. The turbulator20 and fin 22 are each made of an aluminum based material of theAluminum Association 3XXX series aluminum alloys.

For assembly of the heat exchanger assembly 10, the turbulator 20 andfin 22 are joined to the tube 12 using a CAB furnace brazing process.During the brazing process, the Cs--Li--Mg content in the compositioncladding 18 liquifies at or about 550° C. and flows through a porousaluminum oxide (Al₂ O₃) layer on the external surface 16 to wet theexternal surface 16. This wetting provides the medium to continue thedispersement of the oxide layer and allows the composition cladding 18to flow into a joint therebetween and create a braze. It should beappreciated that the CAB furnace brazing process is conventional andknown in the art. It should also be appreciated that plates andmanifolds (not shown) may have the composition cladding 18 to allowfluxless brazing for evaporators.

Additionally, a method, according to the present invention, of assemblyof the heat exchanger assembly 10 is illustrated in FIG. 4. The methodincludes the steps of providing at least one tube 12 having an internalsurface 14 and an external surface 16 and applying a compositioncladding 18 having at least lithium and magnesium to either one of theinternal surface 14 or external surface 16. The method includesdisposing at least one component 20,22 adjacent the composition cladding18 and joining the at least one tube 12 and at least one 20,22 componenttogether using a controlled atmosphere brazing (CAB) process.

In the CAB process, the heat exchanger assembly 10 is placed on a brazeholding furnace fixture 30 and preheated, for example, to a temperaturein a range from about 425° to about 475° F. (224°-246° C.). The heatexchanger assembly 10 and braze holding furnace fixture 30 aretransferred to a prebraze chamber where it is soaked for about 3-15minutes at about 750° F. (399° C.). Subsequently, the hot heat exchangerassembly 10 and braze holding furnace fixture 30 are transferred to aconveyor 32 and moved through a CAB furnace 34 which is purged byapplying a nitrogen gas at 34 inside the CAB furnace 36.

The method includes adding an active metal getter source 38 in the CABfurnace 36 to remove residual oxygen and water vapor in the nitrogen gas34. The active metal getter source 38 may be located upstream of thenitrogen gas, as a solid source 38 affixed to the braze holding furnacefixture 30, or applied as a coating 38 on the braze holding furnacefixture 30 or as a secondary gas purification system (not shown). Theactive metal getter source 38 may be Titanium, Titanium-alloys,Zirconium and Zirconium alloys. For example, the active metal gettersource 38 may be zirconium iron (ZrFe), zirconium nickel (ZrNi) orTitanium Molybdenum (TiMo) used in combination with composition cladding18 to getter residual oxygen and water vapor from the nitrogen gas toless than twenty parts per million (20 ppm). The Ti getter source is Tione hundred weight percent (100 wt %) and the TiMo getter source is Tieighty-five weight percent (85 wt %)/ Mo fifteen weight percent (15 wt%). The Zr getter source is Zr one hundred weight percent (100 wt %) andZrFe getter source is Zr seventy to eighty weight percent (70-80 wt%)/Fe twenty to thirty weight percent (20-30 wt %) and ZrNi gettersource is Zr seventy to eighty weight percent (70-80 wt %)/Ni twenty tothirty weight percent (20-30 wt %). The ZrFe, ZrNi and TiMo gettersource are most efficient in removing residual water vapor and oxygen inthe temperature range from about 400° C. to about 600° C. which iswithin the temperature range of the CAB furnace. It should beappreciated that the CAB furnace 36 has a hot zone 40 from about 595° C.to about 605° C.

In the CAB furnace 36, the heat exchanger assembly 10 is kept for 2-3minutes at about 1095°-1130° F. (591°-610° C.). The brazed heatexchanger assembly 10 is then cooled, removed and applied for itsintended use.

The subsequent example will further demonstrate the unique compositioncladding 18 used with the active metal getter source 38 to fluxlessbraze the heat exchanger assembly 10 using the CAB process.

EXAMPLE ONE

Fluxless brazing was achieved using an active metal getter source 38 ina nitrogen gas 34 atmosphere between an Al/Si/Li and Al/Mn/Mgcomposition cladding 18 on a Aluminum Association series aluminum alloytube 12 and an unclad 3003 aluminum tube in the CAB furnace 36. Thecomposition cladding 18 contained 0.01 to 0.5 wt % Lithium and the corematerial contained up to 0.5 wt % Magnesium. A standard CAB braze cyclewas used to braze test samples in a fluxless CAB process.

The present invention has been described in an illustrative manner. Itis to be understood that the terminology which has been used is intendedto be in the nature of words of description rather than of limitation.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, within the scope of theappended claims, the present invention may be practiced other than asspecifically described.

What is claimed is:
 1. A heat exchanger assembly comprising:at least onetube having an internal surface and an external surface; a compositioncladding having at least lithium and magnesium and elemental cesiumapplied to either one of said internal surface and external surface ofsaid at least one tube; and at least one component disposed adjacentsaid composition cladding, whereby the at least one tube and at leastone component are joined together during a controlled atmosphere brazingprocess.
 2. A heat exchanger assembly as set forth in claim 1 whereinsaid at least one tube comprises an aluminum based material.
 3. A heatexchanger assembly as set forth in claim 2 wherein said aluminum basedmaterial is selected from the Aluminum Association 1XXX, 3XXX, 5XXX and6XXX series aluminum alloys.
 4. A heat exchanger assembly as set forthin claim 1 wherein said composition cladding comprises lithium (Li)within a range from about 0.01% to about 0.3%, magnesium (Mg) within arange from about 0.2% to about 0.7%, sodium (Na) within a range fromabout 0.01% to about 0.1%, silicon (Si) within a range from about 4% to13%, manganese (Mn) within a range from about 0% to about 1%, copper(Cu) within a range from about 0.01% to about 0.1%, zinc (Zn) within arange from about 0% to about 0.3%, beryllium (Be) within a range fromabout 0.01% to about 0.7%, other impurities not exceeding a total of 1%,balance aluminum.
 5. A heat exchanger assembly as set forth in claim 4wherein said elemental cesium (Cs) is within a range from about 0% toabout 2%.
 6. A heat exchanger assembly as set forth in claim 5 whereinsaid lithium (Li) ranges from about 0.01% to about 0.5%.
 7. A heatexchanger assembly as set forth in claim 6 wherein said magnesium (Mg)ranges from about 0.1% to about 2%.
 8. A heat exchanger assembly as setforth in claim 1 wherein said at least one component comprises aturbulator disposed within said tube adjacent said composition claddingon said internal surface.
 9. A heat exchanger assembly as set forth inclaim 1 wherein said at least one component comprises a fin disposedadjacent said composition cladding on said external surface.
 10. A heatexchanger assembly as set forth in claim 1 wherein said at least onecomponent comprises an aluminum based material of the AluminumAssociation 3XXX series aluminum alloys.
 11. A method for assembly of aheat exchanger for an automotive vehicle, said method comprising thesteps of:providing at least one tube having an internal surface and anexternal surface; applying a composition cladding having at leastlithium and magnesium and elemental cesium to either one of the internalsurface or external surface; disposing at least one component adjacentthe composition cladding; and joining the at least one tube and at leastone component together using a controlled atmosphere brazing (CAB)process.
 12. A method as set forth in claim 11 including the step ofapplying a nitrogen gas during the CAB process prior to said step ofjoining.
 13. A method as set forth in claim 12 including the step ofadding an active metal getter source to remove oxygen and water vapor inthe nitrogen gas.
 14. A method as set forth in claim 13 wherein theactive metal getter source is selected from the group comprised ofZirconium (Zr), Zirconium Iron (ZrFe), Zirconium Nickel (ZrNi), Titanium(Ti) and Titanium Molybdenum (TiMo).
 15. A method as set forth in claim11 wherein the at least one tube is selected from the AluminumAssociation 1XXX, 3XXX, 5XXX and 6XXX series aluminum alloys.
 16. Amethod as set forth in claim 11 wherein the composition claddingcomprises lithium (Li) within a range from about 0.01% to about 0.3%,magnesium (Mg) within a range from about 0.2% to about 0.7%, sodium (Na)within a range from about 0.01% to about 0.1%, silicon (Si) within arange from about 4% to 13%, manganese (Mn) within a range from about 0%to about 1%, copper (Cu) within a range from about 0.01% to about 0.1%,zinc (Zn) within a range from about 0% to about 0.3%, beryllium (Be)within a range from about 0.01% to about 0.7%, other impurities notexceeding a total of 1%, balance aluminum.
 17. A method as set forth inclaim 16 wherein the elemental cesium (Cs) is within a range from about0% to about 2%.
 18. A method as set forth in claim 11 wherein the atleast one component comprises a turbulator disposed within the tubeadjacent the composition cladding on the internal surface.
 19. A methodas set forth in claim 11 wherein the at least one component comprises afin disposed adjacent the composition cladding on the external surface.20. A method as set forth in claim 11 wherein the at least one componentcomprises a core material of the Aluminum Association 3XXX seriesaluminum alloys.